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Laboratory 7Brain AnatomyGoals:Describe the organization & function of the three meningeal layers.Explain where cerebrospinal fluid is found in the central nervous systemIdentify the major structures of the human brain using models.Identify the major structures of the sheep brain by dissection.Identify selected cranial nerves on the human and sheep brains.1. Coverings of the Brain:The brain and spinal cord are protected bymultiple layers of tissue.Most external is theskin, followed by the skull.Underneath theskull are three layers of connective tissuemembranes collectively referred to asmeninges.The outer most layer is called thedura mater(literally, hard or tough mother).Itis a tough, double-layered membrane.The mostsuperficial layer of the dura mater forms theinner periosteum of the cranial bones.Themiddle layer, thearachnoid mater(thinkspider) has a delicate spider web-likeappearance and helps to cushion the brain.Theinnermost layer, thepia mater(literally softmother), is a thin, waterproof layer that adheres to the outer surface of the brain and spinal cord.Identification:On the sheep brain, identify the three layers of the meninges.Identify & remove the dura and arachnoid maters.2. Regions of the Brain:The cerebral hemispheres form the largest part of the human brain and are situated above most otherbrain structures. They are covered with a cortical layer with many bumps and grooves called thecerebrum.The visible part of the cerebrum is theneocortex.Interior to thecortex is themidbrain.Underneath the cerebrum lies thebrainstem, resembling handle underneath the main portion of thebrain.At the rear of the brain, beneath the cerebrum and behind the brainstem, is thecerebellum, astructure with a much finer bumps than the cerebrum. The same structures are present in othermammals, although the cerebellum is not so large relative to the rest of the brain.
During development, the brain develops from three expansions of the embryonic neural tube referredto as theforebrain(also called the proencephalon),midbrain(mesencephalon), andhindbrain(rhombencephalon).The forebrain forms the largest region of the human brain form forming thetelencephelonorcerebrum, and thediencephalon.The diencephalon becomes thethalamusandhypothalamuscontrolling movement and autonomic/endocrine function, respectively.The midbrainis the smallest region and is located between the forebrain and hindbrain.The midbrain contains anumber of nuclei involved in relaying auditory and visual information and in regulating voluntarymuscle movement.The hindbrain is closest to the spinal cord and forms thecerebellum,pons, andmedulla oblongata.Figure 2.Developmental brain regions in the mammalian brain.Some brain systems transverse multiple brain regions.For example, voluntary movement begins in theneocortex, but normal voluntary movement also requires input from the cerebellum and midbrain andsignals are relayed in the thalamus.